Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bug Fix: Move heat_timeout variable higher"
  - Bug Fix: Move heat_timeout variable higher

    If a heat_template was used by a testcase the heat_timeout
    variable was not getting initialized and that caused errors
    in the Shade python module.

    JIRA: YARDSTICK-1027

    Change-Id: Ic0bf15b13cc00595964a97f8150dc5e6f2b7e1d7
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index e73f637..639981d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit e73f63767dcba5e3406a8a70a76e36d06fc38479
+Subproject commit 639981d1a2c30a3501749dfe4a7a50609e05cb0b